One of most important requirements of a next generation wireless access system is to support high data transmission rate requirements. To this end, various technologies such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), a relay, etc. have been developed.
A conventional wireless access system considers only one carrier although bandwidths in uplink and downlink are set in different ways. For example, there is provided a wireless communication system in which the number of carriers included in each of uplink and downlink is one and bandwidths in uplink and downlink are generally symmetric, based on a single carrier.
However, in order to satisfy relatively high data transmission rate requirements to ensure a widebandwidth in consideration of an actual state in which frequency resources are saturated, the system is designed to satisfy basic requirements for operating independent systems in distributed bands and carrier aggregation (CA) whereby a plurality of bands is bonded to one system has been introduced.
Here, a carrier in a bandwidth unit in which independent operations are available may be referred to as a component carrier (CC). In order to increase transmission capacity, recent 3GPP LTE-A or 802.16m has continuously extended up to 20 MHz or more. In this case, one or more CCs are aggregated to support a wideband. For example, when one CC supports a bandwidth of 5 MHz, 10 MHz, or 20 MHz, a maximum of 5 CCs are bonded to support a system bandwidth up to a maximum of 100 MHz.
When CA technology is used, data can be simultaneously transmitted and received via various uplink/downlink CCs. Thus, a UE may monitor and measure all CCs.